Coupling multi-channel laser to multicore fiber

ABSTRACT

Aspects described herein include a method comprising arranging a laser die on a substrate. The laser die has multiple channels that are arranged with a first planar arrangement proximate to a facet of the laser die. The method further comprises aligning a single lens to the facet, and aligning a multicore optical fiber to the laser die through the single lens. The multicore optical fiber has a plurality of optical cores that are arranged with a second planar arrangement. Aligning the multicore optical fiber to the laser die comprises rotationally aligning the multicore optical fiber to align the second planar arrangement with the first planar arrangement.

TECHNICAL FIELD

Embodiments presented in this disclosure generally relate to opticaldevices, and more specifically, to techniques for coupling amulti-channel laser to a multicore optical fiber.

BACKGROUND

To support increased bandwidth requirements, optical devices may includeincreasing numbers of optical channels. However, using single-channeloptical fibers such as single-mode fiber (SMF) orpolarization-maintaining fiber (PMF) for the multiple optical channelsoccupies a large volume for fiber management, as well as reduces thechannel density at the fiber termination, which may require increasedpackaging size and/or may affect the spacing of components withinpackaging of a given size.

Multicore fibers can significantly reduce a fiber count within thepackaging, and in some cases may have a same outer diameter assingle-mode optical fibers. However, solutions for optical coupling withthe optical cores of the multicore fiber, such as photonic light-wavecircuits that fan-in to the relatively small pitch between the opticalcores, may impose significant material and/or process costs.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above-recited features of the presentdisclosure can be understood in detail, a more particular description ofthe disclosure, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate typicalembodiments and are therefore not to be considered limiting; otherequally effective embodiments are contemplated.

FIGS. 1A, 1B, and 1C illustrate exemplary implementations of a multicoreoptical fiber, according to one or more embodiments.

FIG. 2 is a diagram illustrating coupling of a multicore optical fiberwith a multi-channel laser die, according to one or more embodiments.

FIG. 3 is a diagram illustrating exemplary alignment of a multicoreoptical fiber, a lens, and a multi-channel laser die, according to oneor more embodiments.

FIG. 4 is an exemplary method of forming an optical device, according toone or more embodiments.

FIG. 5 is an exemplary method of rotationally aligning a multicoreoptical fiber to align with a multi-channel laser die, according to oneor more embodiments.

FIGS. 6A, 6B, and 6C illustrate an exemplary sequence of forming anoptical device within a Transistor Outline (TO) CAN package, accordingto one or more embodiments.

FIGS. 7A, 7B, and 7C illustrate an exemplary sequence of forming anoptical device within a box-type Transmitter Optical Sub-Assemblypackage, according to one or more embodiments.

FIG. 8 is a diagram illustrating an exemplary optical alignment of amulticore optical fiber, according to one or more embodiments.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements disclosed in oneembodiment may be beneficially used in other embodiments withoutspecific recitation.

DESCRIPTION OF EXAMPLE EMBODIMENTS Overview

One embodiment presented in this disclosure is a method comprisingarranging a laser die on a substrate. The laser die has multiplechannels that are arranged with a first planar arrangement proximate toa facet of the laser die. The method further comprises aligning a singlelens to the facet, and aligning a multicore optical fiber to the laserdie through the single lens. The multicore optical fiber has a pluralityof optical cores that are arranged with a second planar arrangement.Aligning the multicore optical fiber to the laser die comprisesrotationally aligning the multicore optical fiber to align the secondplanar arrangement with the first planar arrangement.

Another embodiment presented in this disclosure is an optical devicecomprising a substrate and a laser die arranged on the substrate. Thelaser die has multiple channels that are arranged with a first planararrangement proximate a facet of the laser die. The optical furthercomprises a single lens aligned to the facet, and a multicore opticalfiber aligned to the laser die through the single lens. The multicoreoptical fiber has a plurality of optical cores that are arranged with asecond planar arrangement. The multicore optical fiber is rotationallyarranged such that the second planar arrangement is aligned with thefirst planar arrangement.

Another embodiment presented in this disclosure is a computer programproduct comprising a computer-readable storage medium havingcomputer-readable program code embodied therewith. The computer-readableprogram code is executable by one or more computer processors to performan operation comprising arranging a laser die on a substrate. The laserdie has multiple channels that are arranged with a first planararrangement proximate to a facet of the laser die. The operation furthercomprises aligning a single lens to the facet, and aligning a multicoreoptical fiber to the laser die through the single lens. The multicoreoptical fiber has a plurality of optical cores that are arranged with asecond planar arrangement. Aligning the multicore optical fiber to thelaser die comprises rotationally aligning the multicore optical fiber toalign the second planar arrangement with the first planar arrangement.

Example Embodiments

Solutions for optical coupling with a multicore optical fiber includephotonic light-wave circuits, which fan-in from separate opticalchannels to the relatively small pitch between the cores of themulticore fiber. However, implementations of optical devices usingphotonic light-wave circuits may tend to occupy a relatively largevolume, and/or may impose significant material and/or process costs.

In some embodiments, a method comprises arranging a laser die on asubstrate. The laser die has multiple channels that are arranged with afirst planar arrangement proximate to a facet of the laser die. Themethod further comprises aligning a single lens to the facet, andaligning a multicore optical fiber to the laser die through the singlelens. The multicore optical fiber has a plurality of optical cores thatare arranged with a second planar arrangement, e.g., arranged linearlywithin the planar arrangement. Aligning the multicore optical fiber tothe laser die comprises rotationally aligning the multicore opticalfiber to align the second planar arrangement with the first planararrangement.

Beneficially, the relatively small pitch between the optical cores ofthe multicore fiber permits a single lens to optically couple all of theoptical cores with the multiple channels of the laser die, providingsuitable optical performance without imposing significant material andprocess costs. The relatively small pitch allows other components to beshared, e.g., a single optical isolator shared by the multiple channels.Further, using the single lens to optically couple the multiple channelsnegates a requirement for a minimum free space channel and/or channelpitch.

FIGS. 1A, 1B, and 1C illustrate exemplary implementations of a multicoreoptical fiber, according to one or more embodiments. More specifically,FIG. 1A represents a cross-section view (or an end view) of a multicoreoptical fiber 100 comprising a plurality of optical cores 105-1, 105-2,105-3, 105-4 (also referred to herein as “cores”) and a cladding 110.The cores 105-1, 105-2, 105-3, 105-4 and the cladding 110 may be formedof any materials providing suitable refractive indeces, as will beunderstood by the person of ordinary skill in the art. The cores 105-1,105-2, 105-3, 105-4 are arranged along a line within the plane depictedin FIG. 1A (also referred to herein as the planar arrangement of thecores 105-1, 105-2, 105-3, 105-4).

Although the multicore optical fiber 100 includes four (4) cores in alinear arrangement, alternative numbers and/or alternative planararrangements of the cores 105-1, 105-2, 105-3, 105-4 are alsocontemplated. For example, FIG. 1B represents a cross-section view (oran end view) of a multicore optical fiber 120 comprising seven (7) cores105-1, 105-2, . . . , 105-7 in a star-shaped planar arrangement. FIG. 1Crepresents a cross-section view (or an end view) of a multicore opticalfiber 130 comprising eight cores 105-1, 105-2, . . . , 105-8 in acircular planar arrangement (e.g., where the cores 105-1, 105-2, . . . ,105-8 are evenly spaced with different radial angles). Other regularand/or irregular planar arrangements are also contemplated (e.g.,rectangular). Further, in some embodiments the multicore optical fibers100, 120, 130 may include one or more elements (e.g., stress rods)arranged relative to the cores 105-1, 105-2, . . . , 105-8 such that themulticore optical fibers 100, 120, 130 are polarization-maintainingmulticore optical fibers.

The multicore optical fibers 100, 120, 130 may have any suitabledimensioning. In one embodiment, the multicore optical fibers 100, 120,130 have an outer diameter d of about 125 microns, although other valuesare also contemplated. Generally, adjacent cores 105-1, 105-2, . . . ,105-8 may have any suitable spacing within the multicore optical fibers100, 120, 130. In some embodiments, a pitch p between adjacent cores105-1, 105-2, . . . , 105-8 may be as large as permitted by the outerdiameter d of the multicore optical fibers 100, 120, 130, as largerspacing may be effective to mitigate interference between opticalsignals carried on the adjacent cores 105-1, 105-2, . . . , 105-8. Inone embodiment, corresponding to the outer diameter d of about 125microns, the pitch p between adjacent cores 105-1, 105-2, . . . , 105-8may be in the tens of microns (e.g., between about 20 microns and about30 microns).

When optically aligning any of the multicore optical fibers 100, 120,130 with a multi-channel laser die, an angular alignment of the cores105-1, 105-2, . . . , 105-8 (e.g., relative alignment of the cores105-1, 105-2, . . . , 105-8 within the plane of the planar arrangement)may be performed using two or more of the cores 105-1, 105-2, . . . ,105-8 that are arranged in a line. Any suitable number of the cores105-1, 105-2, . . . , 105-8 are contemplated. For example, four (4)cores 105-1, 105-2, 105-3, 105-4 (shown as angular alignment group 115)may be used for angular alignment of the multicore optical fiber 100,three (3) cores 105-2, 105-5, 105-7 (shown as angular alignment group125) may be used for the multicore optical fiber 120, and two (2) cores105-3, 105-7 (shown as angular alignment group 140) may be used for themulticore optical fiber 130. Notably, not all of the cores 105-1, 105-2,. . . , 105-8 arranged in a particular line need be used for angularalignment (e.g., selecting two or three of the cores 105-1, 105-2,105-3, 105-4 for the multicore optical fiber 100), and the selected onesof the cores 105-1, 105-2, . . . , 105-8 need not be adjacent to eachother within the line. Further, the line in which the cores 105-1,105-2, . . . , 105-8 are arranged need not pass through a center of themulticore optical fibers 100, 120, 130, as with the angular alignmentgroup 135 comprising the cores 105-1, 105-8.

FIG. 2 is a diagram 200 illustrating coupling of a multicore opticalfiber 205 with a multi-channel laser die 210 (also referred to herein as“laser die”), according to one more embodiments. The featuresillustrated in the diagram 200 may be used in conjunction with otherembodiments. For example, the multicore optical fiber 205 may representany of the multicore optical fibers 100, 120, 130 that are depicted inFIGS. 1A, 1B, 1C. Note that the various components and the relativearrangement of the components are not drawn to scale in the diagram 200.

The laser die 210 may include any semiconductor-based laser. In someembodiments, the laser die 210 is formed using III-V material layersthat are epitaxially grown on a substrate (e.g., a silicon substrate).The laser die 210 includes a plurality of channels 215-1, 215-2, 215-3,215-4, each of which is configured to generate and deliver opticalenergy. The optical energy delivered by the plurality of channels 215-1,215-2, 215-3, 215-4 may have the same or differing wavelengths. Theplurality of channels 215-1, 215-2, 215-3, 215-4 are arranged with aplanar arrangement proximate to a facet 220 of the laser die 210. Thefacet 220 of the laser die 210 may be formed using any suitabletechniques, such as etching, mechanical sawing, surface grinding, and soforth. In one example, the channels 215-1, 215-2, 215-3, 215-4 areformed as optical waveguides that extend to the facet 220 (e.g.,terminate at the facet 220). In another example, the optical waveguidesextend close to the facet 220 (e.g., within a few microns), such thatoptical energy exiting the optical waveguides propagates partly throughanother semiconductor material (e.g., silicon) to exit the facet 220.

In the diagram 200, a single lens 225 and a single optical isolator 230are arranged between the laser die 210 and the multicore optical fiber205. The lens 225 may be formed of any suitable materials and may haveany suitable dimensioning. The lens 225 is aligned to the facet 220.Optical energy exits the channels 215-1, 215-2, 215-3, 215-4, which isshown in the diagram 200 respectively as optical signals 235-1, 235-2,235-3, 235-4 (collectively or generically referred to as opticalsignal(s) 235). The optical energy is directed through the lens 225,through the optical isolator 230, and toward an endface 240 of themulticore optical fiber 205.

To ensure that each of the cores 105-1, 105-2, 105-3, 105-4 opticallyalign with a respective one of the channels 215-1, 215-2, 215-3, 215-4,the multicore optical fiber 205 may be rotationally aligned with thelaser die 210, such that the planar arrangement of the cores 105-1,105-2, 105-3, 105-4 is aligned with the planar arrangement of theplurality of channels 215-1, 215-2, 215-3, 215-4. In some embodiments, asix (6)-axis alignment is performed to optically align the multicoreoptical fiber 205 with the laser die 210. Notably, an angular alignmentof the cores 105-1, 105-2, 105-3, 105-4 would not be performed foraligning a single core optical fiber. In some embodiments, the planararrangement of the cores 105-1, 105-2, 105-3, 105-4 corresponds to aplane of the endface 240.

The multicore optical fiber 205 may be rigidly attached with the laserdie 210 when rotationally aligned (e.g., using an adhesive or weldingprocess). Thus, when the multicore optical fiber 205 is rotationallyaligned with the laser die 210, the channel 215-1 provides the opticalsignal 235-1 to the core 105-1, the channel 215-2 provides the opticalsignal 235-2 to the core 105-2, and so forth.

In some embodiments, the pitch between adjacent cores 105-1, 105-2,105-3, 105-4 and/or the pitch between adjacent channels 215-1, 215-2,215-3, 215-4 is small enough that some or all of the optical componentsmay be shared between the cores 105-1, 105-2, 105-3, 105-4 and/or thechannels 215-1, 215-2, 215-3, 215-4. As shown in the diagram 200, thesingle lens 225 and the single optical isolator 230 are shared by all ofthe cores 105-1, 105-2, 105-3, 105-4 and the channels 215-1, 215-2,215-3, 215-4. In some embodiments, the pitch between adjacent channels215-1, 215-2, 215-3, 215-4 is small enough that the offset of thechannels 215-1, 215-2, 215-3, 215-4 from the optical axis of the lens225 contributes only negligible aberration without degrading opticalcoupling, when compared with an on-axis optical system.

Using these techniques, packaging density may be increased as feweroptical fibers, optical isolators, lenses, and/or laser dies are neededwhen optically coupling the laser die 210 and the multicore opticalfiber 205. Further, material and/or process costs during manufacturingmay be reduced as fewer components are used, which also corresponds tofewer optical alignment processes.

As discussed above, the various components and their relativearrangement are not drawn to scale in the diagram 200. In someembodiments, and as shown in the diagram 200, the pitch between adjacentchannels 215-1, 215-2, 215-3, 215-4 is greater than the pitch betweenadjacent cores 105-1, 105-2, 105-3, 105-4. However, in otherembodiments, the pitch between adjacent channels 215-1, 215-2, 215-3,215-4 may be less than or equal to the pitch between adjacent cores105-1, 105-2, 105-3, 105-4.

For example, FIG. 3 is a diagram 300 illustrating an exemplary alignmentof a multicore optical fiber, a lens, and a multi-channel laser die,where a pitch between adjacent channels is less than a pitch betweenadjacent cores. The features illustrated in the diagram 300 may be usedin conjunction with other embodiments. For example, diagram 300represents one possible implementation of the optical system shown inFIG. 2.

In the diagram 300, an inset portion 305 shows the optical signals235-1, 235-2, 235-3, 235-4 exiting the facet 220 of the laser die. Theoptical signals 235-1, 235-2, 235-3, 235-4 are incident on the lens 225and directed toward the endface 240 of the multicore optical fiber. Aninset portion 310 shows the optical signals 235-1, 235-2, 235-3, 235-4being received at the endface 240. Although not shown here, an opticalisolator may be arranged between the lens 225 and the endface 240.

The optical signals 235-1, 235-2, 235-3, 235-4 exit along a length ofthe facet 220 having a distance d2, and the optical signals 235-1,235-2, 235-3, 235-4 are received along a length of the endface 240having a distance d1. In some embodiments, the endface 240 of themulticore optical fiber and the facet 220 of the laser die are parallel,and adjacent ones of the optical signals 235-1, 235-2, 235-3, 235-4 areequidistant at the endface 240 and at the facet 220.

The lens 225 provides a given magnification imaging the mode size of theoptical signals 235-1, 235-2, 235-3, 235-4 exiting the facet 220 of thelaser die onto the mode size of the cores at the endface 240. In someembodiments, the magnification of the lens 225 is positive.

The magnification of the lens 225 also affects the pitch betweenadjacent cores of the optical fibers. For example, in a case where thelens 225 has a magnification M=3 the pitch between the opticalwaveguides of the laser die should be three (3) times narrower than thepitch of the cores in the multicore optical fiber. In some embodiments,the distance d1 is between about 60-90 microns, which for animplementation having four (4) linearly arranged cores corresponds to apitch between about 20-30 microns between adjacent cores. Other valuesof the distance d1 are also contemplated. The distance d2 may have anysuitable value, e.g. based on the design of the optical system,including the magnification of the lens 225. For example, the distanced2 may be approximately 30 microns, which corresponds to anapproximately 10 micron pitch between adjacent channels.

The size of the lens 225, the spacing between the lens 225 and themulticore optical fiber, and the spacing between the lens 225 and thefacet 220 may be selected based on the distances d1, d2. In someembodiments, aligning the multicore optical fiber to the laser diethrough the lens 225 comprises arranging the multicore optical fiber ata distance d4 from the lens 225. The distance d4 is based on amagnification of the lens 225 and is selected to (i) match a mode sizeof the multiple channels to a mode size of the plurality of opticalcores, and (ii) match a pitch between adjacent channels of the multiplechannels to a pitch between adjacent cores of the plurality of opticalcores.

In some embodiments, the distance d4 between the lens 225 and themulticore optical fiber (i.e., the endface 240) is between about two (2)times and about five (5) times a distance d3 between the lens 225 andthe facet 220. In one non-limiting example, the pitch between adjacentcores of the plurality of optical cores is between about 20 and 30microns, the distance d4 is about 3000 microns, and the second distanceis about 1000 microns. For this combination of distances d3, d4, arelatively large aperture of the lens 225 is capable of supporting themultiple channels. When compared with the distances d3, d4, therelatively small offset of the channels 215-1, 215-2, 215-3, 215-4 fromthe optical axis of the lens 225 contributes only negligible aberrationwithout degrading optical coupling, when compared with an on-axisoptical system.

FIG. 4 is an exemplary method 400 of forming an optical device,according to one or more embodiments. The method 400 may be used inconjunction with other embodiments, e.g., to form the optical systemshown in FIG. 3.

The method 400 begins at block 405, where a multi-channel laser die isarranged on a substrate. The substrate may be formed of any suitablematerial, such as silicon or ceramic. In some embodiments, arranging themulti-channel laser die comprises epitaxially growing III-V materiallayers on the substrate. In other embodiments, the multi-channel laserdie is attached to another substrate, and arranging the multi-channellaser die comprises attaching the substrates together (e.g., bonding,soldering).

At block 415, a single lens is aligned to the facets of themulti-channel laser die either actively or passively. At block 425, amulticore optical fiber is aligned to the multi-channel laser diethrough the single lens.

In some embodiments, aligning the multicore optical fiber to themulti-channel laser die comprises arranging the multicore optical fiberat a first distance from the single lens, wherein the first distance isbased on a magnification of the single lens and is selected to (i) matcha mode size of the multiple channels to a mode size of the plurality ofoptical cores, and (ii) match a pitch between adjacent channels of themultiple channels to a pitch between adjacent cores of the plurality ofoptical cores.

In some embodiments, aligning the multicore optical fiber to themulti-channel laser die comprises rotationally aligning the multicoreoptical fiber, which aligns a planar arrangement of a plurality ofoptical cores with a planar arrangement of multiple channels of themulti-channel laser die (block 430).

In some embodiments, the multicore optical fiber is rigidly attachedwith the multi-channel laser die when rotationally aligned, for example,by applying and curing an adhesive or welding process. The method 400ends following completion of block 425.

FIG. 5 is an exemplary method 500 of rotationally aligning a multicoreoptical fiber to align with a multi-channel laser die, according to oneor more embodiments. The method 500 may be used in conjunction withother embodiments, e.g., within block 430 of FIG. 4.

The method 500 begins at block 505, where first spatial coordinates aredetermined for the multicore optical fiber, at which a first channel hasa maximum optical coupling with a first optical core. At block 515,second spatial coordinates are determined for the multicore opticalfiber, at which a second channel has a maximum optical coupling with asecond optical core. The first spatial coordinates and/or the secondspatial coordinates may be represented as two dimensions or threedimensions. In some embodiments, the first optical core and the secondoptical core are furthest from each other along a particular dimension.However, the first optical core and the second optical core may beselected according to any other suitable techniques. Further, in otherembodiments, spatial coordinates may be calculated for more than twooptical cores of the multicore optical fiber.

At block 525, a rotational angle for the multicore optical fiber isdetermined using the first spatial coordinates and the second spatialcoordinates. In some embodiments, the multicore optical fiber is rotatedaccording to the rotational angle and/or spatially translated. In someembodiments, the multicore optical fiber is spatially translated toaveraged spatial coordinates, e.g., at a midpoint between the firstspatial coordinates and the second spatial coordinates.

At block 535, it is determined that the rotation angle corresponds to anoptical coupling, for at least one of the plurality of optical cores,that is less than a threshold value. In some embodiments, thedetermination is responsive to measurements of test optical signalstransmitted from the multi-channel laser die. Generally, the opticalcoupling being less than the threshold value indicates that anunsuitable optical coupling exists for the at least one optical core. Atblock 545, different spatial coordinates are determined for one or bothof the first channel and the second channel. The method 500 may returnto block 525 using the different spatial coordinates, and may proceeduntil the determined rotational angle corresponds to a suitable opticalcoupling for each of the optical cores. In some embodiments, determiningthe suitable optical coupling comprises determining a spatial balancebetween the first spatial coordinates and the second spatial coordinates(e.g., if not aligning exactly with the pitch of the multicore opticalfiber). The method 500 ends following block 545.

FIGS. 6A, 6B, and 6C illustrate an exemplary sequence of forming anoptical device within a Transistor Outline (TO) CAN package, accordingto one or more embodiments. The features illustrated in diagrams 600,615, and 625 may be used in conjunction with other embodiments. Forexample, a process of assembling the TO CAN package may operate tooptically align the components of the optical system shown in FIG. 2.Note that the various components and the relative arrangement of thecomponents are not drawn to scale in the diagrams 600, 615, and 625.

In the diagram 600, the laser die 210 is mounted to a base 605(representing a first housing component) and conductively connected withleads 610 providing external connectivity to the TO CAN package. Thebase 605 may be formed of any suitable material, such as a metal. Insome embodiments, the laser die 210 is arranged on a substrate, whichmay operate as a submount that is attached to the base 605 (i.e.,arranged on the first housing component). In some embodiments, thesubmount provides electrical connections between the laser die 210 andthe leads 610.

In the diagram 615, a cap 620 (representing a second housing component)is contacted to the base 605, such that the laser die 210 is arranged inan interior space formed by the base 605 and the cap 620. The cap 620may be formed of any suitable material, such as a metal. The lens 225 isarranged at an opening of the cap 620. As discussed above, the lens 225may have a positive magnification that images the mode size of theoptical signals 235 exiting the laser die 210 onto the mode size of thecores of the multicore optical fiber 205. By translating the cap 620relative to the base 605, the lens 225 may be aligned to a facet of thelaser die 210 in two spatial dimensions. Once the lens 225 is aligned tothe facet, the cap 620 may be rigidly attached to the base 605 (e.g.,through welding).

In the diagram 625, a surface 640 of an optical connector 635 iscontacted to a surface 630 of the cap 620. The optical connector 635 mayhave any suitable implementation, such as a fiber pigtail or areceptacle. The multicore optical fiber 205 is rigidly attached to theoptical connector 635. In some embodiments, the multicore optical fiber205 is inserted into an interior space 645 of the optical connector 635,and retained by the optical connector 635 using any suitable means, suchas an adhesive, a friction fit, and so forth.

In some embodiments, the optical isolator 230 is arranged in theinterior space 645 and is aligned with the multicore optical fiber 205when inserted. By translating and/or rotating the optical connector 635relative to the cap 620, the multicore optical fiber 205 may be aligned,through the optical isolator 230 and the lens 225, to the facet of thelaser die 210 in three spatial dimensions (and rotationally). Once themulticore optical fiber 205 is aligned to the facet, the opticalconnector 635 may be rigidly attached to the cap 620 (e.g., throughwelding). In this way, aligning the multicore optical fiber 205 to thelaser die 210 comprises attaching the optical connector 635 with ahousing component (e.g., attached with the base 605 through the cap620).

FIGS. 7A, 7B, and 7C illustrate an exemplary sequence of forming anoptical device within a box-type Transmitter Optical Sub-Assembly (TOSA)package, according to one or more embodiments. The features illustratedin diagrams 700, 725, and 730 may be used in conjunction with otherembodiments. For example, a process of assembling the box-type TOSApackage may operate to optically align the components of the opticalsystem shown in FIG. 2. Note that the various components and therelative arrangement of the components are not drawn to scale in thediagrams 700, 725, and 730.

In the diagram 700, the box-type TOSA package comprises sidewalls 705,an interior surface 710 arranged within the sidewalls 705, and a base715 attached to the sidewalls 705. The box-type TOSA package may beformed of any suitable materials. For example, the sidewalls 705, theinterior surface 710, and/or the base 715 may be formed from metals suchas a nickel-cobalt ferrous alloy, cold-rolled steel, or acopper-tungsten composite. In some embodiments, exterior surfaces of thesidewalls 705 may be gold-coated.

An opening 720 is defined through one of the sidewalls 705. Although notdepicted, the box-type TOSA package may further comprise conductiveleads attached to the base 715 and providing external connectivity tothe box-type TOSA package.

The laser die 210 is mounted to the interior surface 710 and isconductively connected with the leads providing external connectivity tothe box-type TOSA package. In some embodiments, the laser die 210 isarranged on a substrate, which may operate as a submount that isattached to the interior surface 710. In some embodiments, the submountprovides electrical connections between the laser die 210 and the leads.

The lens 225 is arranged within the interior space defined by thesidewalls 705, at the opening 720. As discussed above, the lens 225 mayhave a positive magnification that images the mode size of the opticalsignals 235 exiting the laser die 210 onto the mode size of the cores ofthe multicore optical fiber 205. By translating the lens 225 relative tothe laser die 210, the lens 225 may be aligned to a facet of the laserdie 210 in three spatial dimensions. Once the lens 225 is aligned to thefacet, the lens 225 may be rigidly attached to a structure within theinterior space defined by the sidewalls 705.

In the diagram 730, a surface 740 of the optical connector 635 iscontacted to a surface 735 of one of the sidewalls 705. By translatingand/or rotating the optical connector 635 relative to the surface 735,the multicore optical fiber 205 may be aligned, through the opticalisolator 230 and the lens 225, to the facet of the laser die 210 inthree spatial dimensions (and rotationally). Once the multicore opticalfiber 205 is aligned to the facet, the optical connector 635 may berigidly attached to the sidewalls 705 (e.g., through welding). In thisway, aligning the multicore optical fiber 205 to the laser die 210comprises attaching the optical connector 635 with a housing component(e.g., attached with the sidewalls 705).

FIG. 8 is a diagram 800 illustrating an exemplary optical alignment of amulticore optical fiber 205, according to one or more embodiments. Thefeatures illustrated in FIG. 8 may be used in conjunction with otherembodiments, e.g., an exemplary connection of the multicore opticalfiber 205 with the optical connector 635 as shown in FIGS. 6C and 7C.

In the diagram 800, a ferrule 805 surrounds the multicore optical fiber205 and ensures alignment of the multicore optical fiber 205 duringconnector mating. The ferrule 805 may be formed of any material havingsuitable rigidity, such as ceramic, stainless steel, plastic, ortungsten carbide. The ferrule 805 and the multicore optical fiber 205may be rigidly attached to each other using any suitable techniques,such as adhesive or crimping. In some cases, an end of the ferrule 805may be polished after rigidly attaching the multicore optical fiber 205,e.g., to provide an improved optical interface.

Once rigidly attached with the multicore optical fiber 205, the ferrule805 is inserted into a split sleeve 810. A connector body 815 surroundsthe assembly of the multicore optical fiber 205, the ferrule 805, andthe split sleeve 810. In some embodiments, the ferrule 805 may bepermitted to rotate within the connector body 815 to support the angularalignment of the cores of the multicore optical fiber 205. In someembodiments, one or more additional optical components may be housedwithin the connector body 815.

Various techniques have been described for optical coupling amulti-channel laser die with a multicore optical fiber, which mayinclude a polarization-maintaining multicore optical fiber. In someembodiments, a single lens is used to couple with multiple channels ofthe laser die, which eliminates a requirement for a minimum free spacechannel or channel pitch. Having a narrower channel pitch permits asingle optical isolator to be shared by all channels.

Certain types of packaging provide relatively large working distances(e.g., about 1 mm object distance from the laser die to the lens, andabout 3-5 mm image distance from the lens to the multicore opticalfiber, in a TO CAN package), which corresponds to a large lens aperturethat supports multiple channels. Although some or all of the multiplechannels have an offset from an optical axis of the optical system, therelatively large working distances contribute only negligible aberrationwithout degrading optical coupling, when compared with an on-axisoptical system.

Further, optical coupling a multi-channel laser die with a multicoreoptical fiber may leverage existing assembly processes forsingle-channel optical coupling. For example, the laser die may bearranged on a substrate, a lens is actively or passively aligned in twodimensions (e.g., placing a cap including the lens), and an active fiberpigtail or receptacle is aligned in three dimensions and activelyrotationally aligned to align the planar arrangements of the channels ofthe laser die and the cores of the multicore fiber. In some cases, thesame materials and assembly equipment may be used as for single-channeloptical coupling.

One exemplary application of the techniques described herein isassembling a multi-channel directly-modulated or continuous-wave laserpackage. Current packaging techniques may include the entire transmitterinside an expensive hermetic package, although only the laser sourcerequires temperature regulation. In contrast, the techniques describedherein enable a single small and inexpensive laser package that supportsall of the laser channels. The package can be efficientlywavelength-stabilized with a single thermoelectric cooler that coolsonly the laser source. With the increase in packaging density, all ofthe laser channels may fit easily into existing transceiver module formfactors.

In the preceding, reference is made to embodiments presented in thisdisclosure. However, the scope of the present disclosure is not limitedto specific described embodiments. Instead, any combination of thedescribed features and elements, whether related to differentembodiments or not, is contemplated to implement and practicecontemplated embodiments. Furthermore, although embodiments disclosedherein may achieve advantages over other possible solutions or over theprior art, whether or not a particular advantage is achieved by a givenembodiment is not limiting of the scope of the present disclosure. Thus,the preceding aspects, features, embodiments and advantages are merelyillustrative and are not considered elements or limitations of theappended claims except where explicitly recited in a claim(s).

Aspects of the present disclosure are described with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems) and computer program products according to embodimentspresented in this disclosure. It will be understood that each block ofthe flowchart illustrations and/or block diagrams, and combinations ofblocks in the flowchart illustrations and/or block diagrams, can beimplemented by computer program instructions. These computer programinstructions may be provided to a processor of a general purposecomputer, special purpose computer, or other programmable dataprocessing apparatus to produce a machine, such that the instructions,which execute via the processor of the computer or other programmabledata processing apparatus, create means for implementing thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

These computer program instructions may also be stored in a computerreadable medium that can direct a computer, other programmable dataprocessing apparatus, or other devices to function in a particularmanner, such that the instructions stored in the computer readablemedium produce an article of manufacture including instructions whichimplement the function/act specified in the flowchart and/or blockdiagram block or blocks.

The computer program instructions may also be loaded onto a computer,other programmable data processing apparatus, or other devices to causea series of operational steps to be performed on the computer, otherprogrammable apparatus or other devices to produce a computerimplemented process such that the instructions which execute on thecomputer or other programmable apparatus provide processes forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality and operation of possible implementations ofsystems, methods and computer program products according to variousembodiments. In this regard, each block in the flowchart or blockdiagrams may represent a module, segment or portion of code, whichcomprises one or more executable instructions for implementing thespecified logical function(s). It should also be noted that, in somealternative implementations, the functions noted in the block may occurout of the order noted in the figures. For example, two blocks shown insuccession may, in fact, be executed substantially concurrently, or theblocks may sometimes be executed in the reverse order, depending uponthe functionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts, or combinations of special purpose hardware andcomputer instructions.

In view of the foregoing, the scope of the present disclosure isdetermined by the claims that follow.

We claim:
 1. A method comprising: arranging a laser die on a substrate,wherein the laser die has multiple channels that are arranged with afirst planar arrangement proximate to a facet of the laser die, whereinthe substrate is arranged on a housing component; aligning a single lensto the facet; and aligning a multicore optical fiber to the laser diethrough the single lens, wherein the multicore optical fiber has aplurality of optical cores that are arranged with a second planararrangement, wherein the multicore optical fiber is attached to anoptical connector, and wherein aligning the multicore optical fiber tothe laser die comprises: attaching the optical connector with thehousing component; and rotationally aligning the multicore optical fiberto align the second planar arrangement with the first planararrangement.
 2. The method of claim 1, wherein the housing component isa base, wherein the single lens is included in a cap configured toattach to the base, and wherein attaching the optical connector with thehousing component comprises attaching the optical connector to the cap.3. The method of claim 1, wherein aligning the multicore optical fiberto the laser die through the single lens comprises: arranging themulticore optical fiber at a first distance from the single lens,wherein the first distance is based on a magnification of the singlelens and is selected to (i) match a mode size of the multiple channelsto a mode size of the plurality of optical cores, and (ii) match a pitchbetween adjacent channels of the multiple channels to a pitch betweenadjacent cores of the plurality of optical cores.
 4. The method of claim3, wherein the first distance is between two (2) times and five (5)times a second distance between the single lens and the facet.
 5. Themethod of claim 4, wherein a pitch between adjacent cores of theplurality of optical cores is between 20 and 30 microns, wherein thefirst distance is 3000 microns, and wherein the second distance is 1000microns.
 6. The method of claim 1, wherein rotationally aligning themulticore optical fiber comprises: determining first spatial coordinatesat which a first channel of the multiple channels has a maximum opticalcoupling with a first optical core of the plurality of optical cores;determining second spatial coordinates at which a second channel of themultiple channels has a maximum optical coupling with a second opticalcore of the plurality of optical cores; and determining a rotationalangle using the first spatial coordinates and the second spatialcoordinates.
 7. The method of claim 6, wherein rotationally aligning themulticore optical fiber further comprises: determining that therotational angle corresponds to an optical coupling, for at least one ofthe plurality of optical cores, that is less than a threshold value; anddetermining different spatial coordinates for one or both of the firstchannel and the second channel.
 8. An optical device comprising: ahousing component; a substrate arranged on the housing component; alaser die arranged on the substrate, wherein the laser die has multiplechannels that are arranged with a first planar arrangement proximate afacet of the laser die; a single lens aligned to the facet; a multicoreoptical fiber aligned to the laser die through the single lens, whereinthe multicore optical fiber has a plurality of optical cores that arearranged with a second planar arrangement; and an optical connectorattached to the multicore optical fiber, wherein the multicore opticalfiber is rotationally arranged such that the second planar arrangementis aligned with the first planar arrangement.
 9. The optical device ofclaim 8, further comprising: a single optical isolator shared by themultiple channels.
 10. The optical device of claim 8, wherein attachingthe optical connector with the housing component operates to align themulticore optical fiber to the laser die.
 11. The optical device ofclaim 8, wherein the housing component is a base, wherein the singlelens is included in a cap attached to the base, and wherein the opticalconnector is attached to the cap.
 12. The optical device of claim 8,wherein the multicore optical fiber is arranged at a first distance fromthe single lens, wherein the first distance is based on a magnificationof the single lens and is selected to (i) match a mode size of themultiple channels to a mode size of the plurality of optical cores, and(ii) match a pitch between adjacent channels of the multiple channels toa pitch between adjacent cores of the plurality of optical cores. 13.The optical device of claim 12, wherein the first distance is betweentwo (2) times and five (5) times a second distance between the singlelens and the facet.
 14. The optical device of claim 13, wherein a pitchbetween adjacent cores of the plurality of optical cores is between 20microns a about 30 microns, wherein the first distance is 3000 microns,and wherein the second distance is about 1000 microns.
 15. A computerprogram product comprising: a computer-readable storage medium havingcomputer-readable program code embodied therewith, the computer-readableprogram code executable by one or more computer processors to perform anoperation comprising: arranging a laser die on a substrate, wherein thelaser die has multiple channels that are arranged with a first planararrangement proximate to a facet of the laser die, wherein the substrateis arranged on a housing component; aligning a single lens to the facet;and aligning a multicore optical fiber to the laser die through thesingle lens, wherein the multicore optical fiber has a plurality ofoptical cores that are arranged with a second planar arrangement,wherein the multicore optical fiber is attached to an optical connector,and wherein aligning the multicore optical fiber to the laser diecomprises: attaching the optical connector with the housing component;and rotationally aligning the multicore optical fiber to align thesecond planar arrangement with the first planar arrangement.
 16. Thecomputer program product of claim 15, wherein the housing component is abase, wherein the single lens is included in a cap configured to attachto the base, and wherein attaching the optical connector with thehousing component comprises attaching the optical connector to the cap.17. The computer program product of claim 15, wherein rotationallyaligning the multicore optical fiber comprises: determining firstspatial coordinates at which a first channel of the multiple channelshas a maximum optical coupling with a first optical core of theplurality of optical cores; determining second spatial coordinates atwhich a second channel of the multiple channels has a maximum opticalcoupling with a second optical core of the plurality of optical cores;and determining a rotational angle using the first spatial coordinatesand the second spatial coordinates.
 18. The computer program product ofclaim 17, wherein rotationally aligning the multicore optical fiberfurther comprises: determining that the rotational angle corresponds toan optical coupling, for at least one of the plurality of optical cores,that is less than a threshold value; and determining different spatialcoordinates for one or both of the first channel and the second channel.19. The method of claim 1, wherein attaching the optical connector withthe housing component operates to rotationally align the multicoreoptical fiber.
 20. The computer program product of claim 15, whereinattaching the optical connector with the housing component operates torotationally align the multicore optical fiber.